Method and system for extensible position location

ABSTRACT

A method and system for extensible positioning that uses a primary reference node at a known first position and a secondary reference node at a second position, where a range is measured between the secondary reference node and the primary reference node. The second position is determined based upon the first position and the measured range. A second range is measured between the secondary reference node and a non-fixed node. A third position corresponding to the non-fixed node is determined based upon the second position and the second range.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/103,438filed on Apr. 12, 2005, now U.S. Pat. No. 7,239,277 B1, which claims thebenefit of U.S. Provisional Application Ser. No. 60/561,154, filed Apr.12, 2004.

GOVERNMENT RIGHTS

The US Government has a paid-up license in this invention and the rightin limited circumstances to require the patent owner to license otherson reasonable terms as provided for by the terms of contractDDAB07-03-D-C213-0003 awarded by the United States Army Communicationsand Electronics Command, Fort Monmouth, N.J. 07703.

FIELD OF THE INVENTION

The present invention relates to positioning systems, and moreparticularly to ranging between two or more nodes having known positionsand a fixed or non-fixed node to determine its position.

BACKGROUND OF THE INVENTION

Ultra wideband (UWB) positioning architectures are known to typicallyinvolve two or more reference radios used to determine the position of atarget radio. Conventional UWB positioning architectures determine theposition of the target radio relative to the position of the referenceradios. In these conventional architectures, each of the referenceradios are generally placed at unique fixed locations and communicatesignals with the target radio to determine the position of the targetradio relative to the reference radios. Typically, the location of eachof the fixed reference radios is determined by some independent method,such as global positioning system (GPS), local survey, or other knownpositioning or mapping systems. When determining the position of thetarget radio, UWB signals are communicated between the target radio andthe reference radios. The distance between a given reference radio andthe target radio can be determined from the time-of-flight of a UWBsignal as the UWB signal travels between the reference radio and thetarget radio, where the time-of-flight can be measured directly ordetermined using various well known angle-of-arrival and/or differentialtime-of-arrival techniques.

However, known UWB systems suffer from various problems. Conventionalsystems do not allow for a quick addition of a new reference node to thepositioning system. Typically, when a reference radio is placed in a UWBpositioning system, the location of the reference node must bedetermined by a time-consuming independent method, such as GPS, prior tousing the reference radio as a reference point. This may cause problemswhere setting up a positioning system is time critical, such as infirefighting or warfare. Additionally, conventional methods ofdetermining the position of a non-fixed radio have insufficient accuracyand may have difficulty in resolving the position of a reference radio,particularly in situations when the radio is moving or which a GPSsignal is blocked such as indoors. Moreover, traditional positioningarchitectures neither readily accept UWB radios nor incorporate theircapabilities.

Additional problems in conventional UWB systems are caused by multipathcharacteristics of UWB signals. Multipath characteristics of a UWBsignal impacts the accuracy of a time-of-flight distance measurement.Conventional time-of-flight distance measurements assume that theamplitude of a transmitted signal is received across a direct pathbetween a transmitter and a receiver, and that the transmitted signalthat follows the direct path is larger than received signals that followan indirect path. Time-of-flight distance measurements also assume thatthe leading edge of the received signal corresponds to the direct pathbetween a transmitter and a receiver. However, these assumptions are notalways correct. Oftentimes, multipath signals may combine with oneanother such that the direct path portion of the signal has a lesseramplitude than combined multipath signals. Also, a direct path betweentwo radios may not exist; in which case a time measurement based on adetermined leading edge of a signal will not correspond to the directpath. In such a situation, a leading edge detection approach thatassumes the leading edge corresponds to the location in the signalhaving the maximum amplitude may incorrectly determine the location ofthe leading edge. Incorrect determination of the leading edge results inerror in the timing measurement, which translates into an incorrectlydetermined distance between the reference radio and the target radiothat, when combined with other distance measurements between the targetradio and other reference radios, further translates into an incorrectlydetermined position of the target radio.

What is needed, therefore, is an extensible positioning architecturethat may quickly add additional radios to determine a position of afixed or non-fixed radio with an acceptable accuracy.

BRIEF SUMMARY OF THE INVENTION

According to the present invention, there is provided an extensiblepositioning system. In embodiments, the system may include sets ofprimary reference nodes, secondary reference nodes, and non-fixed nodes.Ranging is performed between the primary and reference nodes todetermine the positions of the secondary reference nodes. The secondaryreference nodes thereby extend the ability of the system to performranging with non-fixed nodes.

In one exemplary embodiment of a method for positioning a node accordingto the invention, a first node is placed at a known first position. Arange is then measured between the first node and a second node and theposition of the second node is determined based upon the first positionand the range. A position of a third node is then determined from theposition of the second node. Either or both the second node and thethird node can be a secondary reference or a non-fixed node.

In another exemplary embodiment, at least one range measurement qualitymetric is associated with at least one range measurement where a rangequality measurement can be a standard deviation, a measurement agemetric, an error region metric, a signal quality metric, an RFenvironment metric, or a ranging geometry metric. An error region metricmay be the number of error region levels or an error region elongationmetric. A signal quality measurement may be a bit error rate or asignal-to-noise ratio. The RF environment metric can be used to select aRF signal propagation model used to calculate a range. A ranginggeometry metric can be an angle acuteness metric or a geometric dilutionof precision metric.

In a further exemplary embodiment of the invention, at least one rangemeasurement quality metric is used to determine a confidence level of aposition determined for a node. In one embodiment of the invention, theconfidence level is compared to at least one other confidence leveldetermined for at least one other position determined for the node toselect the most acceptable determined position of the node.

In one embodiment, the third node determines its own position. In analternative embodiment, the position of the third node is determined byanother node such as a base station. In one embodiment, ranginginformation is filtered prior to determining a position to removeranging noise.

In a preferred embodiment, the first node, the second node, and thethird node include an Ultra Wideband radio.

In another exemplary embodiment of the invention, a position locationsystem includes a first node having a known first position, a secondnode having a second position determined based upon a range measuredbetween the second node and the first node, and a third node having athird position determined based upon said second position. Either orboth the second node and the third node can be a secondary reference ora non-fixed node.

In one embodiment, the position location system associates at least onerange measurement quality metric with at least one range measurement.

In a further exemplary embodiment of the invention, the positionlocation system uses at least one range measurement quality metric todetermine a confidence level of a position determined for a node. In oneembodiment of the invention, the confidence level is compared to atleast one other confidence level determined for at least one otherposition determined for the node to select the most acceptabledetermined position of the node.

In a preferred embodiment, the first node, the second node, and thethird node include an Ultra Wideband radio.

These and additional features and advantages of the present inventionwill become more apparent from the detailed description set forth belowwhen taken in conjunction with the drawings in which like referencecharacters generally identify corresponding elements throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate embodiments of the present inventionand, together with the description, further serve to explain theprinciples of embodiments of the invention.

FIG. 1 illustrates an exemplary embodiment of a Position Location System(PLS) in accordance with the invention.

FIG. 2 illustrates an exemplary embodiment of deploying the positioninglocation system and developing a node map according to the presentinvention.

FIG. 3 illustrates ranging by position location system of FIG. 2 toexemplary non-fixed nodes.

FIG. 4A illustrates two possible positions of a node determined givenrange measurements with two reference nodes.

FIG. 4B illustrates a two-dimensional position of a node determinedgiven range measurements with three reference nodes.

FIG. 5 illustrates an exemplary error band.

FIG. 6 illustrates an exemplary error region.

FIG. 7A illustrates an exemplary probability density function of timemeasurement error.

FIG. 7B illustrates an exemplary probability density function ofdistance measurement error.

FIG. 7C illustrates exemplary probability density functions overlaidover an error region.

FIG. 7D illustrates an exemplary joint probability density function.

FIG. 7E illustrates exemplary probability density functions overlaidover an error region.

FIG. 7F illustrates an exemplary joint probability density function.

FIG. 7G illustrates an exemplary first error region compounding with anexemplary second error region to produce a composite error region.

FIG. 7H illustrates an exemplary third error region compounding with thecomposite error region of FIG. 7G.

FIG. 8 illustrates exemplary acute angles between a node and referencenodes.

FIG. 9 illustrates an exemplary elongated error region.

FIG. 10A illustrates an exemplary PLS using a secondary reference nodeto determine a position.

FIG. 10B illustrates an exemplary PLS using a non-fixed node as asecondary reference node.

FIG. 10C illustrates an exemplary node in near alignment with referencenodes.

FIGS. 11A-11C illustrate an exemplary embodiment of deploying anextensible PLS according to the present invention.

FIG. 12 illustrates an exemplary embodiment of the architecture of anUWB radio included in the base station and the primary, secondary, andnon-fixed nodes according to the present invention.

FIG. 13 illustrates an exemplary embodiment of a layout of a RF moduleof an UWB radio according to the present invention.

FIG. 14 illustrates an exemplary embodiment of a layout of a developmentmodule of an UWB radio according to the present invention.

FIG. 15 illustrates an exemplary embodiment of a top-level systemsoftware architecture of the PLS according to the invention.

FIG. 16 illustrates an exemplary embodiment of a base stationapplication architecture according to the present invention.

FIG. 17 illustrates an exemplary embodiment of the solver according tothe present invention.

FIG. 18 illustrates an exemplary embodiment of a non-fixed node displayapplication architecture of a non-fixed node according to the presentinvention.

FIG. 19 illustrates an exemplary embodiment of a radio controllerapplication according to the present invention.

FIG. 20A illustrates an exemplary embodiment of a time division multipleaccess superframe and time slot according to the present invention.

FIG. 20B illustrates an exemplary embodiment of the range request packet2024 according to the present invention.

FIG. 21 illustrates an exemplary embodiment of a computing environment2100 for the PLS according to the present invention.

FIG. 22 illustrates an exemplary process performed by the PLS accordingto the present invention.

FIG. 23 illustrates an exemplary process of performing distancecalculations by using a non-fixed node as a secondary reference node fora certain period of time according to the present invention.

FIG. 24 illustrates another exemplary process of using a non-fixed nodeas a secondary reference node for a certain period of time according tothe present invention.

It should be understood that these figures depict embodiments of theinvention. Variations of these embodiments will be apparent to personsskilled in the relevant art(s) based on the teachings contained herein.For example, the flow charts contained in these figures depictparticular operational flows. However, the functions and steps containedin these flow charts can be performed in other sequences, as will beapparent to persons skilled in the relevant art(s) based on theteachings contained herein.

DETAILED DESCRIPTION OF THE INVENTION

The invention is a novel position location system in a defined or ad-hocwireless network distributed in and around a coverage area such asinside a structure. In the following description, numerous specificdetails are set forth in order to provide a thorough understanding ofthe present invention. In other instances, well known communicationtechniques have not been described in particular detail to avoidunnecessarily obscuring the invention. As herein defined, communicationsmeans transmission or reception of a signal with or without modulatedinformation.

The present invention implements UWB radio communications technologiesin a positioning architecture to improve the accuracy over knownpositioning systems and to further resolve positioning problems that areotherwise irresolvable, such as, but not limited to, providing a systemfor extensible positioning of non-fixed UWB radios (nodes).

An UWB radio provides a platform for solutions and improvements toconventional positioning systems. Briefly, basic UWB radio transmitterstypically emit short pulses with tightly controlled averagepulse-to-pulse intervals where the pulse may involve one or many cycles.In the widest bandwidth embodiments, UWB radios transmit a monocyclepulse resembling the first derivative of a Gaussian pulse. Narrowerbandwidth embodiments of UWB radio transmitters may instead emit burstsof cycles, where the burst of cycles may be shaped in accordance with adesired envelope. Various types of UWB waveforms and methods of waveformshaping are described in U.S. Pat. No. 6,026,125 (issued Feb. 15, 2000)to Larrick, Jr. et al, which is incorporated herein by reference in itsentirety.

One type of UWB radio is referred to as an impulse radio. Impulse radioswere first fully described in a series of patents, including U.S. Pat.No. 4,641,317 (issued Feb. 3, 1987), U.S. Pat. No. 4,813,057 (issuedMar. 14, 1989), U.S. Pat. No. 4,979,186 (issued Dec. 18, 1990) and U.S.Pat. No. 5,363,108 (issued Nov. 8, 1994), all to Larry W. Fullerton.These patent documents are incorporated herein by reference in theirentireties.

The earliest impulse radio systems typically used pulse positionmodulation. Pulse position modulation is a form of time modulation inwhich the value of each instantaneous sample of a modulating signal iscaused to modulate the position in time of a pulse. For impulse radiocommunications, the pulse-to-pulse interval is varied on apulse-by-pulse basis by two components: an information component and apseudo-random code component. The pseudo-random component is similar tothose in spread spectrum systems. Typically, spread spectrum systemsmake use of pseudo-random codes to spread the normally narrowbandinformation signal over a relatively wide band of frequencies. A spreadspectrum receiver correlates these signals to retrieve the originalinformation signal. However, unlike spread spectrum systems, thepseudo-random code for impulse radio communications is not necessary forenergy spreading because the monocycle pulses themselves have aninherently wide information bandwidth. Instead, the pseudo-random codein impulse radio communications is used for channelization, for energysmoothing in the frequency domain, and for jamming resistance.

UWB radio systems such as impulse radio systems can vary pulsecharacteristics other than time position for modulation purposes. M-aryversions of phase modulation, frequency modulation, amplitudemodulation, alone and in combination with pulse position modulation havebeen proposed and implemented as described in U.S. Pat. No. 5,748,891(issued May 5, 1998) to Fleming et al., U.S. Pat. No. 6,133,876 (issuedOct. 17, 2000) to Fullerton et al., and U.S. Pat. No. 6,700,939 (issuedMar. 2, 2004) to McCorkle et al. These patent documents are incorporatedherein by reference in their entireties.

UWB radio systems such as impulse radio systems can also vary pulsecharacteristics other than time position for channelization purposes.U.S. Pat. No. 6,700,939 (issued Mar. 2, 2004) to McCorkle et al.describes use of combinations of inverted and non-inverted pulses todefine user channels. U.S. Pat. No. 6,603,818 (issued Aug. 5, 2003) toDress, Jr. et al. describes use of combinations of different pulsewidths to define user channels and use of orthogonal pulse types todefine multiple data channels within user channels. U.S. patentapplication Ser. No. 09/638,192 by Roberts et al. discloses varyingpulse amplitude and pulse type to define user channels. These patentdocuments are incorporated herein by reference in their entireties.

The UWB radio receiver can be a direct conversion receiver with a crosscorrelator front end. The cross correlator front end coherently convertsan electromagnetic train of pulses to a baseband signal in a singlestage. The baseband signal is the basic information channel for thebasic UWB radio communications system, and is also referred to as theinformation bandwidth. The data rate of the UWB radio transmission isonly a fraction of the periodic timing signal used as a time base. Eachdata bit modulates many pulses of the periodic timing signal yielding atrain of pulses for each data bit. The cross correlator of the impulseradio receiver integrates the train of pulses to recover the transmitteddata bit. Two forms of homodyne impulse radio receivers are known in theart including the impulse radios of Fullerton et al., previouslyincorporated by reference, which involve correlation of received signalswith template signals generated by the receiver, and a transmittedreference impulse radio where the impulse radio transmitter transmitspulses in pairs spaced apart in time by a known time delay(s) where thereceiver coherently correlates a delayed received signal with thereceived signal. A transmit reference impulse radio is described in U.S.Pat. No. 6,810,087 (issued Oct. 26, 2004) to Hoctor et al, which isincorporated herein by reference.

The UWB radio receiver can alternatively be a threshold detector typesystem where pulses having amplitude greater than the detectionthreshold of a detector diode are transmitted and received. Examples ofthreshold detector type impulse radio systems are described in U.S. Pat.Nos. 3,662,316 (issued May 9, 1972) to Robbins and U.S. Pat. No.6,690,741 (issued Feb. 10, 2004) to Larrick et al, both of which areincorporated herein by reference.

The present invention implements a Position Location System (PLS) usingUWB radio transceivers that both transmit and receive UWB signals. Theuse of transceivers in the PLS described herein is not intended to limitthe scope of the invention, which can be practiced using variouscombinations of transmit-only, receive-only, and transceiver devices.The PLS is a user deployable system that provides easily interpreted,real-time, highly accurate range matrix information to both a userwithin a building and incident command personnel remote to the building.The invention may be used within and around man-made buildings, such ashouses or office structures, but is not limited to these areas. Thepresent invention may also be used in other natural structures and openareas so long as signals may be communicated between UWB radios. Thefollowing section gives a general overview of the invention.

FIG. 1 illustrates an exemplary embodiment of a position location system(PLS) according to the present invention. A vehicle 120 may be used totransport and place a base station 104 alongside a building 100. Thebase station 104 includes direction finding antenna arrays 105A-B and106A-B that are positioned facing the building 100. In between the basestation 104 and building 100, are primary reference nodes 102A-102C. Ina preferred embodiment, the primary reference nodes 102A-102C are placedat fixed, known locations that are unique from one another and the basestation 104. In this embodiment, a primary reference node includes anUWB radio placed at a fixed position. Each of the UWB radios of theprimary reference nodes 102A-102C has an antenna for communicating UWBsignals with the base station 104. The UWB signals are communicated todetermine the location of the base station 104 relative to the primaryreference nodes 102A-102, as will be discussed later in detail.Typically, the primary reference nodes 102A-102C are placed by a person,but may be placed by a non-fixed remote control device (e.g., a robot).

In accordance with the invention, secondary reference nodes 108A-108Jare positioned at fixed yet typically arbitrarily selected unknownlocations, which may be inside or outside building 100. Each secondaryreference node 108A-108J includes an UWB radio having an antenna forcommunicating with each other, the primary reference nodes 102A-102C,and the base station 104. The secondary reference nodes 108A-108J rangewith one another and the primary reference nodes 102A-102C to developpositioning data for constructing a node map, as will be discussed laterin detail. Like a primary reference node, a secondary reference node'sposition is fixed and can be used to determine the position of anothernode. However, whereas a primary reference node has a known location(position), a secondary reference node has a location determined by aranging process. As such, a location determined using primary referencesis more accurate than one determined using one or more secondaryreferences due to ranging errors, as further described below.

Also shown within the building 100 are non-fixed nodes 110A-110B. Thenon-fixed devices 110A-110B may move within and outside of the building100 and each include an UWB radio. At any given time, the non-fixednodes 110A-110B may be moving or stationary. Each non-fixed node110A-110B may include a handheld display for a user, and may alsoinclude the functionality of a personal digital assistant (PDA). In oneembodiment, the non-fixed nodes 110A-110B are personal tracking unitsthat are transported by a person and incorporated into, for example, ahandheld unit, a helmet unit, or a backpack unit. In an alternativeembodiment, the non-fixed devices 110A-110B are associated with orincorporated into a movable remote controlled platform (e.g., a robot)that includes a video camera that allows a remote user to direct thenon-fixed device. As is the case with a secondary reference node, theposition of a non-fixed node is determined by a ranging process. Thenon-fixed node is normally not used as a reference node since it may bemoving. However, exceptions are described herein where a non-fixed nodemay be used as a secondary reference node due to certain circumstances.

FIG. 2 illustrates an exemplary embodiment of deploying the positioningsystem and developing a node map according to the present invention.After the base station 104 and the primary reference nodes 102A-102Chave been positioned alongside the building 100, the base station 104and the primary reference nodes 102A-102C range with one another todetermine their relative positions. The ranging process between the basestation 104 and the primary reference nodes 102A-102C involvesdetermining a signal direction and a distance.

To determine the signal direction, the base station 104 uses thedirection finding antenna arrays 105A-105B and 106A-106B mounted on thevehicle in a two-dimensional (2-D) or three-dimensional (3-D)arrangement. The direction finding antenna arrays 105A-105B and106A-106B are adapted to make Angle-of-Arrival (AOA) measurements on UWBsignals transmitted by the primary reference nodes 102A-102C. Thedirection finding antenna arrays 105A-105B and 106A-106B measure the AOAfor the received signals to determine from which direction each of theprimary reference nodes 102A-102C is transmitting. Typically, theprimary reference nodes 102A-102C are within a Line-of-Sight (LOS) ofthe direction finding antenna arrays 105A-105B and 106A-106B. However,the base station 104 may use other techniques that measure the receptiontime or signal strength of the transmitted signal to differentiatebetween received multipath signals to determine the angle of arrival, asis understood by those of skill in the art. In an alternativeembodiment, the antenna arrays 105A-105B and 106A-106B are not requiredto be direction finding antennas. This alternative AOA approach isdescribed in U.S. Pat. No. 6,760,387 (issued Jul. 6, 2004) to Langfordet al., which is incorporated herein by reference in its entirety.

While the base station 104 is making AOA measurements, the base station104 and the primary reference nodes 102A-102C are also measuring thedistance between one another. In one embodiment, UWB signals are used todetermine the distance between the base station 104 and the primaryreference nodes 102A-102C. To determine the distances between eachprimary reference node 102A-102C and the base station 104, each primaryreference node either individually, sequentially, or at the same time,transmits an UWB signal to the base station 104. The distance between aprimary reference node and the base station 104 can be determined fromthe time-of-flight of the UWB signal between the primary reference nodeand the base station, using any one of various approaches involvingone-way or round-trip signal transmission(s). These various approachestypically require identifying the leading edge of the received signal,which normally corresponds to the direct path between the nodes. Otherapproaches that are not based on leading edge detection, such as theranging approach described in U.S. Pat. No. 6,111,536 (issued Aug. 29,2000) to Richards et al., which is incorporated herein by reference inits entirety, require a direct path to exist between nodes to determinedistance. Alternatively, the distance between two nodes can bedetermined based on signal amplitude as described in U.S. Pat. No.6,700,538 (issued Mar. 2, 2004) to Richards, which is incorporatedherein by reference in its entirety.

In the distance determination, the ranging process may or may notrequire synchronization between the base station 104 and the primaryreference nodes 102A-102C. For the one-way ranging process, the primaryreference nodes 102A-102C and the base station 104 may share a commonclock signal, or may each have their own individual clocks and perform asynchronization process. In an alternative embodiment, the base station,upon receiving a signal from a primary reference node, may send anacknowledgement signal back to the primary reference node. When theprimary reference node receives the acknowledgement signal, the primaryreference node determines a round trip time to the base station anddetermines the distance to the base station based on the round triptime. This two-way ranging process does not require the primaryreference node and base station to be synchronized. In a furtheralternative embodiment, the base station 104 may transmit an UWB signalthat is received by the primary reference nodes 102A-102C, which eachsend acknowledgement signals from which the base station 104 measuresround trip times and determines distances to the primary referencenodes. It is noted that either the base station or the primary referencenode may determine the distance therebetween. Round trip rangingtechniques are further described in U.S. Pat. No. 6,133,876 (issued Oct.17, 2000) to Fullerton et al., and various combinations of one-way andround trip ranging approaches are described in U.S. Pat. No. 6,300,903(issued Oct. 9, 2001) to Richards et al., each of which is incorporatedherein by reference in its entirety. Another alternative embodimentinvolves differential time of arrival (DTOA) techniques as described inU.S. Pat. No. 6,054,950 (issued Apr. 25, 2000) to Fontana, which isincorporated herein by reference.

Once the ranging process is complete, the base station 104 and eachprimary reference node 102A-102C store the relative distances to oneanother in a range matrix. The range matrix stores a group of one ormore distance measurements to one or more nodes, and a nodeidentification (ID) that corresponds to distance measurement to each ofthe one or more nodes. The range matrix includes relative distance andnode ID information for each node that the node communicates with, aswell as an age of the distance data and a quality of range measurementmetric(s) as described below. For example, in the present embodiment,the range matrix of the base station 104 includes a node ID for each ofthe primary reference nodes 102A-102C. For the node ID of primaryreference node 102A, the range matrix includes a distance measurementbetween the base station 104 and the primary reference node 102A.Similar information is included for primary reference nodes 102B-102C.Likewise, at the primary reference node 102A, the range matrix of theprimary reference node 102A includes a node ID for each of the primaryreference nodes 102B-102C and for the base station 104, and alsoincludes a distance measurement for each. In an alternative embodiment,the range matrix stores a timing measurement between each of the primaryreference nodes 102A-102C and the base station 104, and a distance isderived from the timing measurement. After the AOA measurements and thedistance between the base station 104 and the primary reference nodes102A-102C are known, the base station 104 uses the range matrix todetermine its position relative to the primary reference nodes 102A-102Crelative, as will be discussed later in detail. The base station may,for example, be the (0,0) coordinate of an x-y coordinate system.Alternatively, a primary reference node or other location may be chosenfor the (0,0) coordinate.

In addition to each node maintaining a range matrix, the nodes may alsoperiodically communicate their range matrix information with other nodesand the base station. Such communication can be performed using UWBcommunications capabilities or using non-UWB communications capabilitiessuch narrowband wireless communications methods. Communication of rangematrix information among nodes enables each node to have information onall other nodes in the PLS, regardless of whether each node can rangewith another node. Rather than transmitting the range information for asingle node, the range matrix can be transmitted, which is a data setincluding ranging information for all nodes within the PLS. Because eachnode maintains a range matrix and can communicate their range matrixinformation, the base station 104 can obtain range information for allnodes by communicating with only one primary reference, secondaryreference, or non-fixed node. The maintenance and communication of rangematrix information among nodes is further discussed in relation to FIGS.20A and 20B. If range information is kept locally, every node cancalculate its own position and communication it to the other nodes.

The base station 104 uses the range matrix information to create aninitial node map that identifies the relative positions of the basestation 104 and the primary reference nodes 102A-102C. In the node map,the primary reference nodes 102A-102C are reference points relative tothe base station 104. The node map is used to develop a graphicalrepresentation of the relative positions of the primary reference nodes102A-102C and the base station 104. A graphical user interface (GUI) isalso included in the base station 104 for displaying to a user thegraphical representation of the node map. A node map view of the GUIdisplays the node map and the locations of the base station 104 and theprimary reference nodes 102A-102C. The graphical representation of thenode map view includes the relative positions of all nodes communicatingdirectly or indirectly with the base station 104. The node map may alsoinclude nodes other than primary reference nodes 102A-102C, as isdiscussed below.

Secondary reference and non-fixed nodes may be added to the PLS. When anode is added, the node undergoes a similar ranging process as thatdescribed above between the primary reference nodes 102A-102C and thebase station 104. To add a node, either the node itself, one of theprimary reference nodes 102A-102C, the base station 104, or anothersecondary reference node initiates the ranging process with the node todetermine the relative distance between them. The ranging processemployed may differ from the ranging process between the primaryreference nodes 102A-102C and the base station 104. For example, theranging between the base station and the primary references may rely ona two-way measurement of time of arrival, whereas, the ranging betweenthe primary and secondary references may use a one way time of arrivalmeasurement or differential time of arrival measurement. It should benoted, however, that the present invention may use any variety of knownranging techniques found suited for a particular positioningapplication. An added node may listen for communicated position and/ormay initiate ranging to other nodes.

In the ranging process for a secondary reference node or non-fixed node,the node (secondary reference or non-fixed) determines its distancesrelative to one or more other nodes, and the determined distances areplaced in a range matrix. The range matrix of the node may include, forexample, distances information to one or more of the primary referencenodes 102A-102C, the base station 104, secondary reference nodes, ornon-fixed nodes. As the ranging process is completed, the range matrixinformation is communicated across the PLS network to the base station104. The base station 104 updates the node map to include relativepositions of the node, similar forming the node map, as described above.

In the preferred embodiment of the PLS described above, the position ofbase station 104 is determined by ranging with the primary referencenodes 102A-102C. As such, the base station could be described as asecondary reference node since it is a fixed node and because itsposition is determined via a ranging process. Although the base stationcould be used as a secondary reference node for ranging with othernodes, after performing ranging to determine its own position relativeto the primary reference nodes, the base station does not performranging with other nodes an instead is devoted to performing otherfunctions as later described.

In an alternative embodiment of the PLS, one or more of the primaryreference nodes 102A-102C may be incorporated into the base station 104,in which case the position of base station 104 is also known relative tothe one or more primary reference nodes 102A-102C. Under such anarrangement the base station could also be described as a primaryreference node since its position is fixed and known. However, with thisembodiment, the base station 104 typically would not perform rangingfunctions, which instead are performed by primary reference nodes102A-102C.

In still another embodiment, the base station 104 itself may beconfigured to act as one or a plurality of primary reference nodes.Under this arrangement, the base station would perform ranging withsecondary reference nodes to establish a 2-D (3-D) coordinate system. Inone exemplary embodiment, the base station node would be a primaryreference node that would typically only perform ranging with the three(or four) secondary reference nodes used to establish the 2-D coordinatesystem. Referring to FIG. 1, under such an arrangement, the vehicle 120may place a base station 104 along side a building 100. Secondaryreferences 102A-102C would be placed at unknown or arbitrary locationrelative to the base station 104. Ranging techniques would be employedto determine the relative locations of the secondary references102A-102C in order to establish a coordinate system. Thereafter,secondary reference nodes 102A-102C would be used to determined rangesto other secondary reference nodes and/or non-fixed nodes.

FIG. 2 provides an example of an extensible position determinationarchitecture. As shown, secondary reference nodes serve as additionalreference points from which the position of either additional secondaryreference nodes or non-fixed nodes can be determined. In FIG. 2,secondary reference nodes 108A and 108B perform ranging with primaryreference nodes 102A-102C. The ranges (or distances) between the primaryand secondary reference nodes are used to determine the positions of thesecondary reference nodes. Once the positions of secondary referencenodes have been determined, their determined position can be used todetermine positions of additional secondary reference nodes or non-fixednodes. As depicted, secondary reference node 108C performs rangingbetween primary reference node 102B and secondary reference nodes 108Aand 108B. Secondary reference node 108D performs ranging with secondaryreference nodes 108A-108C.

FIG. 3 illustrates an exemplary embodiment of tracking movement ofnon-fixed nodes 110A-110B within the building 100 according to thepresent invention. Similar to adding the secondary reference nodes108A-108C to the PLS, the non-fixed nodes 110 also range with the basestation and the primary and secondary reference nodes to determine theirrelative positions. Since the non-fixed nodes 110A-110B may move, theranging process is repeated periodically in order to appropriatelyupdate the range matrix information and the node map to reflect themovement of the non-fixed nodes.

In one exemplary embodiment, the non-fixed nodes 110A-110B maysimultaneously range with three or more primary reference nodes102A-102C, three or more secondary reference nodes 108A-108D, or anycombination of three or more primary and secondary reference nodes toestablish a two-dimensional or three-dimensional coordinate system.Similar to the process discussed for the primary and secondary referencenodes, the non-fixed nodes 110A-110C also range with the other nodes bycommunicating UWB signals. From the communicated UWB signals, distancesbetween the non-fixed nodes 110A-110B and the primary reference nodes102A-102C and/or secondary reference nodes 108A-108D are determined.

Once the distances are determined, the non-fixed nodes 110A-110B updatea range matrix that includes a node ID and a determined distance to eachof the nodes, as described above. However, the base station, the primaryreference nodes, and the secondary reference nodes may also determinethe distance to the non-fixed node to update their range matrix. Therange matrix information can be relayed to the base station 104 fromeither of the non-fixed nodes 110A-110B, the primary reference nodes102A-102C, or the secondary reference nodes 108A-108D. In oneembodiment, the secondary reference nodes 108A-108D relay the rangematrix information to the base station 104 through the primary referencenodes 102A-102C. In this embodiment, the secondary reference nodes108A-108C collect and transmit range matrix data from multiple nodes(primary, secondary, and non-fixed) and transmit the range matrixinformation to the primary reference odes 102A-102C. However, in analternative embodiment, the secondary reference nodes 108A-108D maydirectly relay the range matrix information to the base station 104. Ina further alternative embodiment, any of the primary, secondary, ornon-fixed nodes relays the range matrix information to the base station104.

Periodically the base station 104 receives range matrix information fromthe primary or secondary reference nodes to update the range matrix ofthe base station 104. The range matrix of the base station 104 may beupdated at specific time intervals, or may be updated when newinformation is detected in the range matrix information, such as, forexample, when a new node is added to the PLS, as described above.Examples of updates include an addition of a new node and itscorresponding range information and a change in information pertainingto a non-fixed node such as its position, location, speed, direction oftravel, and changes in any of these. The base station 104 uses the rangematrix to calculate the relative positions of all of the nodes, and, ifnecessary, to update the node map to reflect any position changes of thenodes. In one embodiment, the base station 104 uses differencing betweena current range matrix and a previous range matrix to determine changesbetween the two. If differences are detected, then the base station maycalculate relative positions for all nodes in the PLS, or alternatively,may only make calculations based on the differences. In a furtheralternative embodiment, certain nodes such as primary reference nodesand secondary reference nodes are updated at a certain frequency, whichis less often than other nodes, such as non-fixed nodes.

After calculating the differences between the range matrices, the basestation 104 discovers range updates, calculates corresponding positionupdates, and updates the display of the GUI to reflect the positionupdates. Once the base station 104 has updated the node map, the nodemap may be transmitted by the base station 104 in the form of a positiontable to the non-fixed nodes, either directly or indirectly, via one ormore primary and/or secondary reference nodes. The position table isreceived by the non-fixed nodes 110A-110B, which can use the positiontable to display icons representing the positions of each of thenon-fixed nodes 110A-110B, primary reference nodes 102A-102C, secondaryreference nodes 108A-108H, and the base station 104 in a GUI similar tothat of the base station 104.

FIG. 4A illustrates an exemplary embodiment of the base station 104using triangulation to determine the location of a secondary referencenode relative to two primary reference nodes according to the presentinvention. Once a node is able to range to two or more other nodes, thelocation of the node may be determined using triangularization and thenode may be placed in the node map. The position of a node can bedetermined through calculating a distance between the node and two (ormore) other nodes using triangularization/multi-lateration to determinea 2-D (or 3-D) position of the node relative to the other nodes.Triangularization may be used to determine the location of any node withrespect to two or more other nodes, such as a primary reference node, asecondary reference node, a base station, or a non-fixed node.

One embodiment uses triangularization to determine the position of asecondary reference node 408 relative to primary reference nodes 402Aand 402B. Either the secondary reference node 408 or one of the primaryreference nodes 402A and 402B initiates a ranging process such as thosedescribed above from which the distance D_(A) between the primaryreference node 402A and the secondary reference node 408 is determinedas well as the distance D_(B) between the primary reference node 402Band the secondary reference node 408. As described above, the distancesbetween the nodes can be determined by either the primary referencenodes 402A and 402B or the secondary reference node 408 depending on theranging process employed and which node initiates it. Once determined,the distances D_(A) and D_(B) are included in the range matrix alongwith node IDs of the respective nodes and are communicated to the basestation. In the calculation at the base station, the distance D_(A) andthe distance D_(B) respectively are radii of circles (or arcs) havingthe respective primary reference nodes 402A-402B at the center. The twocircles intersect at two locations 422 and 422′, which correspond to thetwo possible locations of the secondary reference node 408. Theambiguity in the location of the secondary reference node 408 may beresolved by entering other known information on the secondary referencenode at the base station, such as removing impossible positions due to aphysical barrier, or other information such as speed, direction,position relative to a known physical barrier, etc. For example, inrelation to FIG. 3, possible location 422′ could be eliminated based ona priori knowledge. For example, a rule may be used that would requiresecondary reference nodes to be placed at locations further away fromthe vehicle 120 than the primary reference nodes. Any location that isfound to violate this rule would be discarded in order to resolve theambiguity. A position ambiguity may also be resolved by ranging withanother primary (or secondary) reference node, as will be describedbelow.

FIG. 4B illustrates an exemplary embodiment using triangulation betweenthree primary reference nodes to determine the location of a secondaryreference node. In this embodiment, the primary reference nodes402A-402C each determine the distance to the secondary reference node408 either by measuring the two-way (round trip) time of arrival or theone-way time of reception. The primary reference node 402A calculatesthe distance D_(A) between the primary reference node 402A and thesecondary reference node 408. Similarly, the primary reference node 402Bcalculates the distance D_(B) between the primary reference node 402Band the secondary reference node 408, and the primary reference node402C calculates the distance D_(C) between the primary reference node402C and the secondary reference node 408. In an alternative embodiment,the secondary reference node 408 calculates the distance between therespective primary reference nodes 402A-402C. The distances D_(A),D_(B), and D_(C) respectively can be used to form circles of radiiD_(A), D_(B), and D_(C) about the respective primary reference nodes402A-402C. All three circles intersect at a single location thatcorresponds to the location of the secondary reference node 408, thusgiving a two dimensional location of the secondary reference node 408.It is noted that the two dimensional location may be used to form athree dimensional location by entering other information about thenon-fixed node, such as a known height, direction of movement, etc.Otherwise, an additional node at a different elevation may be used todetermine a three-dimensional location for the non-fixed node, as isunderstood by those of skill in the art. Alternatively, various devicessuch as altimeters, electronic compasses, magnetic compasses, and othernavigational devices can be used to determine elevation of a node. Asimilar triangulation process is used to determine the location of thenon-fixed nodes using a combination of any three primary or secondaryreference nodes. The present triangularization embodiments are intendedto illustrate the invention, and are not intended to be exhaustive. Itis noted that any combination of distances between the base station,primary reference nodes, secondary reference nodes, and non-fixed nodesmay be used in triangularization, as is understood by those skilled inthe art.

FIG. 5 illustrates an exemplary embodiment of an error in determiningthe distance between a primary reference node 502 and a non-fixed node510 using UWB signals according to the present invention. Duringranging, the primary reference node 502 transmits an UWB signal to thenon-fixed node 510 to determine the distance from the primary referencenode 502 to the non-fixed node 510, which corresponds to the distance D.As illustrated, a primary reference node 502 is ranging to a non-fixednode 510 with the primary reference node 502 being at the center of acircle 540 with a radius D. A measured time of flight for UWB signalstranslates to a distance D between the primary reference node 502 andthe non-fixed node 510. However, a certain amount of error occurs inthis determination, as illustrated by the circle 542 of radius D+d andthe circle 544 of radius D−d. The accuracy of a given distancecalculation depends on the accuracy of the time clock used by theprimary reference node 502 and/or by the non-fixed node 510, dependingon which node performs the calculation and whether a one-way orround-trip signal transmission approach is used or not. The accuracy ofa given distance calculation may also be impacted by the speed of signalpropagation through a given multipath environment (e.g., through aconcrete or sheet rock wall). Although, such ‘propagation’ errors couldalso be used to assess ranging error, for simplicity UWB signals areassumed to propagate at the speed of light regardless of the propagationpath. Given this assumption, a time measurement is only as accurate asthe clock(s) used by the measuring node(s), where a time-based distancemeasurement has a related distance measurement error for each timemeasurement period. The error band is caused by imprecision in thetiming measurement, which results in a distance measurement error of ±dcausing an error band where the non-fixed node 510 is determined to belocated a distance D±d apart from primary reference node 502 asrepresented by the error band.

FIG. 6 illustrate an exemplary embodiment of an error region about adetermined (calculated) position, which results from the distancemeasurement errors of three range measurements used to determinedistances between three reference nodes and a non-fixed node accordingto the present invention. Primary reference nodes 602A-602C arerespectively positioned at distances D_(A), D_(B), and D_(C) relative tothe non-fixed node 610. The primary reference nodes 602A-602C arelocated at the respective centers of circles of radius D_(A), D_(B), andD_(C). Each of the determined distances from the primary reference nodes602A-602C to the non-fixed node 610 has an Error Band (EB), depicted asEB₁ for primary reference node 602A, EB₂ for primary reference node602B, and EB₃ for primary reference node 602C. The EB is associated withtiming measurement errors, as described above. When three (or more)distances are calculated using timing measurements, an error region 608is formed at the intersection of the error bands EB₁, EB₂, and EB₃,within which the non-fixed node 610 is located. Also shown areenlargements of the error region 608 to further illustrate theintersection of the error bands EB₁, EB₂, and EB₃.

FIGS. 7A-7B illustrate exemplary embodiments of probability functionsfor timing measurement errors and distance measurement errors accordingto the present invention. Time measurement error may be modeled as aprobability function. As shown in FIG. 7A, a Gaussian-like probabilityfunction models the time measurement error in picoseconds (ps). Timingmeasurements are often within some constant time error, e.g., ±10picoseconds, where the time measurement error corresponds to a distancemeasurement error, ±d_(error) as shown in FIG. 7B. This distancemeasurement error can be accounted for in impulse positioningcalculations. In this embodiment, most of the timing error is within ±10picoseconds, but a non-zero probability of error exists that the timingerror is greater than 10 picoseconds. Ideally, the probability functionwould be very narrow and steep around zero, with the outermost edges ofthe probability function along the x-axis being very close to zero.However, the probability function may have less of a hump than depicted,and may also approach being flat. It should also be understood thatprobability functions are not necessarily symmetrical and may notgenerally have a Gaussian-like shape, as is understood by those ofordinary skill in the art.

FIG. 7B illustrates an exemplary embodiment of a probability function ofthe distance measurement error according to the present invention. Asdepicted, the distance error is shown as a Gaussian-like probabilityfunction, with a majority of the error within a distance ±d. Thisimplies that for a given time measurement, the distance error is mostlikely less than a distance d away from a reference. The zero referenceshown in FIG. 7B would correspond to the determined distance when usedwith the invention. In other words, a probability function like thatshown in FIG. 7B would span the cross section of an error band. It isagain noted that the most probable correct distance is not necessarilyat the center of the error band, and depends on the shape of probabilitydensity function used. As shown, the distance error is greater than thedistance d for a small non-zero probability.

Given probability density functions for each error band used in aposition calculation, a joint probability density function can bedetermined to identify a most likely position of a node within the errorregion. FIG. 7C depicts the probability density function 708 of FIG. 7Bbeing applied for each of the three error bands of FIG. 6 where eachprobability density function 708 is overlaid across a cross section oferror region 608 corresponding to one of the error bands. Whenmultiplied together the three probability functions produce a jointprobability density function 712, which resembles a three dimensionalsurface, as shown in FIG. 7D. Because all three probability functions708 used correspond to a traditional Gaussian distribution, the peak ofthe resulting joint probability density function 712 is at its centerand thus the determined position 714 of the non-fixed node correspondsto the center of the error region. However, the probability densityfunctions used can vary from each other in shape, amplitude, or in someother manner as necessary in which case the peak of the resulting jointprobability density function may not correspond to the center point ofthe error region. FIG. 7E presents an example where one of theprobability density functions 716 is skewed such that it is notsymmetrical around a center point. As shown in FIG. 7F, this skewing ofone of the probability density functions results in the peak of theresulting joint probability function 718 also being skewed and thus thedetermined position 720 of the non-fixed node corresponds to a pointthat is not at the center of the error region.

Having described the concept of an error region about a positiondetermined based upon ranging measurements relative to primary referencenodes, the concept of compounding ranging error in accordance with theinvention is now described. Basically, compounding ranging errorinvolves calculating a position based on ranging measurements relativeto at least one other position that was also calculated based on rangingmeasurements. Referring again to FIG. 6, the error region 608 is shownrelative to three known positions of reference nodes 602A-602C. Had anyone of the three primary reference nodes 602A-602C been a secondaryreference node then the position of the secondary reference node woulditself be within some error region such that the position of thenon-fixed radio 610 would be within a larger composite error region.

An example of compounding ranging error is shown in FIG. 7G. In FIG. 7G,an error region 608 corresponds to ranging error with one of the primaryreference nodes of FIG. 6 instead being a secondary reference nodehaving an error region 722. Thus, each point within error region 608 mayvary in accordance with error region 722. As such, error region 722 canbe repeatedly placed about the perimeter of error region 608 to producea composite error region 724 boundary. As additional secondary referencenodes are used, additional ranging error is compounded. FIG. 7H depictsan example of an additional layer of compounding ranging error where anadditional primary reference node of FIG. 6 is instead a secondaryreference node having a ranging error region 726. As with the priorexample, the ranging error is placed about the perimeter of (composite)error region 724 to produce (composite) error region 728. It isimportant to note that the outer boundary of (composite) error region728 is the same regardless of the order in which the ranging errors oferror regions 722 and 726 are compounded with error region 608.

In addition to inaccuracies in distance caused by timing measurements,the accuracy of a positioning calculation can also be adversely impactedby the locations of the primary or secondary reference nodes relative tothe non-fixed node. Specifically, if an angle between a pair of primaryand/or secondary reference nodes and the non-fixed node is excessivelyacute (i.e., approaches 0°), the accuracy of the calculation used todetermine the location of the non-fixed node can be unacceptable. Thissituation typically occurs when a non-fixed node is a significantdistance away from the primary and/or secondary reference nodes and alsooccurs whenever a non-fixed node is at a position in near alignment(i.e., on the same line) with two (or more) reference nodes.

FIG. 8 illustrates an exemplary embodiment of acute angles betweenmultiple primary reference nodes relative to a non-fixed node accordingto the present invention, where for simplicity and clarity purposes,nodes are represented as diamond dipole antennas. As shown, each anglebetween every pair of primary reference nodes 802A-802-D with respect toa non-fixed node 810 forms an acute angle θ. As depicted, the angleθ_(AB) is between primary reference nodes 802A and 802B, the angleθ_(AC) is between primary reference nodes 802A and 802C, the angleθ_(AD) is between primary reference nodes 802A and 802-D, the angleθ_(CD) is between primary reference nodes 802C and 802-D, the angleθ_(BC) is between primary reference nodes 802B and 802C, and the angleθ_(BD) is between primary reference nodes 802B and 802-D. Using one ormore excessively acute angles in the position calculation elongates theerror region from the timing measurement, as described below.

FIG. 9 illustrates an exemplary embodiment of an elongated error region908 resulting from using one or more excessively acute angles in theposition calculation according to the present invention. In thisembodiment, the intersection of error bands EB₁-EB₃ forms an elongatederror region 908. The elongated error region 908 results fromexcessively acute angles being between each pair of primary (orsecondary) reference nodes relative to the non-fixed node 910. Thiscauses the error bands EB₁-EB₃ to overlap such that the resulting errorregion is elongated along an axis generally perpendicular to the averagedirection of the references relative to the non-fixed node.Consequently, the positioning error in the direction of the elongationcan be significant, and may result in unacceptable positioning accuracy.Moreover, as the non-fixed node 910 travels farther away from theprimary or secondary reference nodes, the angles with the primary orsecondary reference node pairs becomes even more acute (i.e., approach0°), which results in further elongation of the error region 908. As thedistance between the non-fixed node and the other nodes increases, thecircles that correspond to the determined distances between thenon-fixed node and the others nodes become increasingly concentric, andat a great enough distance, multiple nodes may be viewed as a singlenode, which lowers the dimension of the position that can be calculated.To overcome these problems, the present invention may use alternatecombinations of nodes to extend the distances at which UWB positioningarchitectures have acceptable positioning accuracy, as described below.Various other geometry-based metrics can also be established to assessposition determination accuracy including Geometric Dilution ofPrecision (GDOP) methods well known in the art.

FIGS. 10A-10B illustrate an exemplary embodiment of an extensible PLStracking non-fixed nodes 1010A-1010C that overcomes the problems inpositioning accuracy. Given that a non-fixed node can be located atexcessively acute angles relative to a given pair of primary (and/orsecondary) reference nodes, and that a direct path between a primary orsecondary reference node and the non-fixed node may not exist, thepresent invention performs alternative positioning calculations basedupon the acceptability of the positions of various combinations ofprimary, secondary, and/or non-fixed nodes relative to the non-fixednode (or secondary reference node) for which a position is to bedetermined. In this embodiment, the nodes of the extensible PLScollaborate with the base station to attain the highest confidence levelin the accuracy of a calculated position for a given node. To accomplishthis, each node maintains a range matrix on other nodes with which itcommunicates to allow the base station 104 to calculate a position for anode with the highest confidence level possible (or desirable). In oneembodiment, a non-fixed node may be used as a secondary reference nodeto calculate the position of another non-fixed node. This may occur whenthe position of the non-fixed node is known and it becomes necessary toextend positioning measurements to another non-fixed node to increaseconfidence levels in a distance calculation.

As shown in FIG. 10A, the primary reference nodes 1002A-1002C and thesecondary reference node 1008A are ranging with and tracking non-fixednode 1010A. In this embodiment, each pair of primary reference nodes1002A-1002C form angles that are not overly acute with respect to thenon-fixed node 1010A, and are also within a direct LOS of the non-fixednode 1010A. The distance measurements result in a small error region,and thus triangularization results in an acceptable positioningmeasurement of the non-fixed node 1010A.

Additionally, the secondary reference node 1008A also has a direct LOSwith the non-fixed node 1010A. To increase the confidence levels in adistance measurement, an additional ranging measurement can be takenbetween the secondary reference node 1008A and the non-fixed node 1010A.Having additional ranging measurements allows the base station 1004 toselect a best available combination of ranging measurementscorresponding to a best possible position calculation given anestablished acceptance criteria, which provides the highest possibleconfidence level of the determined position of the non-fixed node 1010A.

Signal quality measurements can also be used to make a determination ofranging measurement accuracy. It is well known, for example, that as thesignal-to-noise ratio (SNR) decreases the determination of a leadingedge of a receiving UWB signal becomes more difficult and prone toerror. Similarly, a high bit-error-rate may indicate high multipath. Inaccordance with the invention, a standard deviation of rangemeasurements higher than a threshold combined with a SNR also higherthan a threshold indicates a non-LOS situation. Thus, in accordance withthe invention, acceptability thresholds can be established for signalquality. Under one arrangement, expected ranging errors are establishedfor a range of SNRs. Metrics may also be established that characterize amultipath environment about a given radio as being in a high multipathenvironment or being in close proximity to an interferer. If RFenvironment characterization metrics are employed, different RF signalpropagation models can be employed to remove ranging error due to signalpropagation being other than the speed of light.

When selecting a best available combination of ranging measurements, thebase station 1004 may consider one or more factors such as signalquality metrics (e.g., SNR, bit error rate, etc.), probability densityfunctions, shape and orientation of an error region, acuteness of anglesbetween reference nodes, age of a range measurement, etc. Under oneembodiment, the number of error regions compounded is used such thatpositions having the least amount of error compounding are considered tobe better than those having more compounding. The acceptance criteriamay include acceptability thresholds and may involve a decision tree(e.g., a flow chart) where the best combination of answers to variousquestions is sought. In order to better manage network load, the basestation 1004 may instruct certain reference nodes to not perform certainranging measurements with a given non-fixed node. For example, whenmanaging the ranging measurements of the PLS, the base station 1004 maydecide a work load of a given reference node is causing it to become abottleneck and provide instructions for it to not perform a rangingmeasurement. In this way, a proper balance between speed of the PLS andaccuracy can be maintained.

In FIG. 10B, primary reference nodes 1002A-1002C and the secondaryreference node 1008A are tracking the non-fixed node 1010B. However inthis embodiment, an obstacle 1006 prevents a direct LOS for the primaryreference nodes 1002B-1002C and the non-fixed node 1010B. Only primaryreference node 1002A and the secondary reference node 1008A have adirect LOS with the non-fixed node 1010B. While a direct LOS does notprevent the primary reference nodes 1002B-1002C from ranging with thenon-fixed node 1010B, the accuracy of the timing measurements will beadversely affected as previously described since the leading edges ofthe received signals would not correspond to direct paths.

To accommodate a non-LOS situation, the current embodiment may insteaduse the calculated positions of one or more of the other non-fixed nodesas a secondary reference node. In this embodiment, a non-fixed node1010A is used by the base station 1004 as a secondary reference node tocalculate the position of a non-fixed node 1010B. For example, aposition of the non-fixed node 1010A, which has LOS to the non-fixednode 1010B, might be selected to calculate the position of non-fixednode 1010B. In such a situation, it is preferable that the position ofthe non-fixed node 1010A remains constant while the non-fixed node isused as a secondary reference node. In addition to LOS, othercharacteristics, such as speed, direction, elevation, or speed inchanges for any of these, may be used to select among non-fixed nodesthat could be used as a secondary reference node.

In FIG. 10C, the primary reference nodes 1002A-1002C and the basestation 1004 are tracking the non-fixed nodes 1010A and 1010B. In thisembodiment, the angles of the primary reference nodes 1002A-1002C withthe non-fixed node 1010B are excessively acute since they are nearalignment. However, non-fixed node 1010A is at a location that formsless of an acute angle with the non-fixed node 1010B relative to any ofthe primary reference nodes 1002A-1002C. Since the primary referencenode pairs form relatively acute angles with the non-fixed node 1010B,the non-fixed node 1010A may be used as a secondary reference node tocalculate the relative position of the non-fixed node 1010B. Generally,although an error region of a position calculated based upon a positionof a non-fixed node (or secondary reference nodes) can be larger thanthe error region of a position calculated based upon known positions ofprimary reference nodes due to compounding ranging error (describedpreviously), the larger error region may be more acceptable than asmaller but excessively elongated error region calculated using primaryreference nodes having overly acute angles.

By using additional nodes, an error region for a position based on oneor more non-fixed nodes and/or secondary reference nodes can bedetermined and compared to the error region about a position based on acalculation exclusively using primary reference nodes, and the positioncalculation having the most acceptable error region can be selected.Thus, by collaborating with other nodes, the base station 1004 canmaintain one or more determined positions and position accuracyconfidence levels. This allows the base station 1004 to select aposition of a node with the highest position confidence level. Thedetermined node positions and their corresponding confidence levels maybe broadcast by the base station 1004 to the primary, secondary, andnon-fixed nodes. Additionally, via collaboration, the calculated andknown positions of the various nodes can be compared for consistency,and anomalies between different node distance determinations can be usedto identify where a direct path does not exist between two nodes. Ifconfidence of range measurements is low, the base station can requestadditional secondary reference nodes be placed in certain approximatelocations in order to improve reference node geometry, signal strength,etc.

The configurations of primary reference nodes, secondary referencenodes, and non-fixed nodes described previously are provided forexemplary purposes only. Generally, primary reference nodes may bepositioned at locations within coverage area such as outside a buildingor inside a building with spacing between primary reference nodesintended to provide acceptable ‘position determination’ accuracy overthe coverage area. For example, if a coverage area encompasses ashopping mall, primary reference nodes may be positioned within eachstore inside the mall and at established intervals in common spaces ofthe mall such that secondary reference nodes are within at least adesired maximum distance from the closest primary reference node(s).Similarly, primary reference nodes may be put on every, for example,third floor within a tall building so as to extend acceptable positiondetermination accuracy to the highest floors. Primary reference nodesmay also positioned to accommodate locations that might otherwise nothave a LOS (i.e., they would be blocked) due to an obstruction. Thus,the invention can be practiced using a multitude of primary referencesnodes (e.g, 10's, 100's, etc.) or with as few as one primary referencenode, where the invention allows the use of secondary reference nodes inconjunction with available primary reference nodes to determine othernode positions within an acceptable level of confidence.

FIGS. 11A-11C illustrate an exemplary embodiment of deploying anextensible PLS according to the present invention. In this embodiment,the extensible and adaptable positioning architecture utilizes UWBradios that are included in non-fixed nodes, primary reference nodes,and secondary reference nodes. FIG. 11A illustrates an exemplaryembodiment of initial setup locations for the base station and theprimary reference nodes according to the present invention. Initially,unique locations 1140 are selected for deployment of the PLS in andaround building 1100. Primary reference nodes 1102A-1102C and a basestation 1104 are placed at fixed locations outside of the building 1100,with the primary reference nodes 1102A-1102C being closer to thebuilding 1100 than the base station 1104. It is noted that otherlocations may be selected for the primary reference nodes 1102A-1102Cand the base station 1104, and that the primary reference nodes1102A-1102C may be placed on different sides of the building 1100, oreven within the building 1100.

In this embodiment, the base station 1104 includes a processing device,such as a portable computer, and an UWB radio. The base station 1104constructs a node map of the base station 1104 and the primary referencenodes 1102A-1102C through the ranging process, as discussed above. Theprimary reference nodes 1102A-1102C and the base station 1104 form thereference system for positioning and tracking of the secondary referenceand non-fixed nodes. As the relative positions between the primaryreference nodes 1102A-1102C and base station 1104 are being calculated,users (e.g., emergency responders, firemen, police, soldiers) carryingthe non-fixed and secondary reference nodes enter the building 1100 andbegin placing the secondary reference nodes. In an alternativeembodiment, the non-fixed node may be associated with a moveable remotecontrolled device (e.g., a robot) that places the secondary referencenodes within the building 1100.

FIG. 11B illustrates an exemplary embodiment of deploying secondaryreference nodes and non-fixed nodes within the building 1100 accordingto the present invention. As a user enters, the user places secondaryreference nodes within the building 1100. As illustrated, the secondaryreference nodes 1108A-1108E are placed at locations 1150. In thisembodiment, two users are shown associated with non-fixed nodes1010A-1010B, respectively, as they place the secondary reference nodes1108A-1108E within the building 1100. As the secondary reference nodes1108A-1108E are positioned and as the non-fixed nodes 1010A-1010B movewithin the building 1100, the primary reference nodes 1102A-1102C, thesecondary reference nodes 1108A-1108E, and the non-fixed nodes1010A-1010B range with one another to determine their relativedistances, as described above. As the nodes determine their relativedistances to one another, the relative distances are included in rangematrix information that is communicated to the base station 1104 eitherdirectly or through the primary reference nodes 1102A-1102C, which thebase station 1104 uses to update the node map. It is noted that more orless secondary or non-fixed nodes may be used, and that the secondaryreference nodes may be placed at other locations, as is understood bythose of skill in the art.

FIG. 11C illustrates an exemplary embodiment of a fully deployed PLSaccording to the present invention. The base station 1104 hasconstructed a node map including the base station 1104, the primaryreference nodes 1102A-1102C, the secondary reference nodes 1108A-1108H,and the non-fixed nodes 1010A-1010B. The primary reference nodes1102A-1102C and the secondary reference nodes 1108A-1108H periodicallyrange with the non-fixed nodes 1010A-1010B to determine their relativedistances, which ranging updates are forwarded to the base station 1104to update the node map. The PLS also allows for non-position relatedcommunications between the base station 1104 and non-fixed nodes1010A-1010B, either directly or via reference nodes, which can be usedfor command and control of personnel actions, status updates,situational alerts, etc.

FIG. 12 illustrates an exemplary embodiment of the architecture of anUWB radio included in the base station and the primary, secondary, andnon-fixed nodes according to the present invention. In this embodiment,the UWB radio includes an antenna 1202, a RF module 1204, and aDevelopment Module 1206. The antenna 1202 is coupled to a RF module1204, which is coupled to the Development Module 1206. The RF module1204 and the Development Module 1206 are mounted within a housing (notshown), which protects the circuit boards and provides mechanicalstability. The housing also provides radio frequency (RF) shielding. Theantenna assembly 1202 mounts to the outside of the enclosure andconnects to the RF input of the RF module 1204.

The RF module 1204 includes a transmit/receive (T/R) switch 1210, a RXGain & Filter Network 1212, and a Pulser/Flipper 1214. The T/R switch1210 is adapted to route RF signals (i.e., control whether signals aretransmitted or received by the antenna), the RX Gain & Filter Network1212 is adapted to reject interference and to provide gain control tothe signal delivered to the Development Module 1206, and thePulser/Flipper 1214 is adapted to generate pulses and selectively invertgenerated pulses thereby allowing pulse-by-pulse control of the polarityof each transmitted pulse. Alternatively, separate transit and receiveantennas could be employed instead of a single antenna and a T/R switch.

To transmit data, Baseband Chip 1228 passes data it receives fromprocessor 1230, FPGA 1232, and/or Processor Peripherals 1234 to theTimer chip 1224B. Timer chip 1224B is adapted to generate ultra-precisetiming triggers that enable time-hopped modulation. The Timer chip 1224Bis clocked by the Reference Oscillator 1222, which also clocks theBaseband chip 1228. A signal is then sent to the Pulser/Flipper 1214that outputs appropriately timed pulses and inverted pulses representingthe data that are passed to the T/R Switch 1210 and output to antenna1202.

When receiving a signal from antenna 1202, T/R switch 1210 routes thereceived signal to RX Gain & Filter Network device 1212 where it isappropriately amplified and filtered. The amplified/filtered signal isthen output to Splitter 1216. At the output of Splitter 1216, the signalis split and transferred to Correlator Chips 1226A-1226B, which receivetiming triggers from Timer Chips 1224A-1224B, respectively. The Timerchips 1224A-1224B are clocked by the Reference Oscillator 1222, which isthe primary oscillator for the system and is used as a phase-lockreference for oscillators 1220A-B. A signal is also sent by Timer Chip1224A to the Calibrator 1218 to calibrate the incoming signal from theRX Gain & Filter Network device 1212. The Correlator chip 1226 convertsthe RF signal to a baseband signal that can be sampled by the BasebandChip 1228. The Correlator chips 1226A-1226B are shielded to minimizeinterference to the correlator circuits. The Baseband chip 1228 is aCMOS logic and multi-ADC (i.e., analog to digital converter) chipresponsible for acquisition, modulation, tracking and scanning functionsof the radio. From the Baseband chip 1228, the data is transferred tothe processor 1230. The processor 1230, along with theField-Programmable Gate Arrays (FPGA) 1232 and the processor Peripherals1234 configures the Baseband chip 1228. The processor 1230 also controlsand monitors the state of the radio during operation and manages datainput/output (I/O) to the user.

FIG. 13 illustrates an exemplary embodiment of a layout of RF module1300 of an UWB radio according to the present invention. Included in RFmodule 1300 are the Power Supplies 1302, RF Module Connector 1304,Receive Circuit 1306, Antenna Port 1308, T/R Switch and Filters 1310,Pulser Inverter 1312, and Pulse Generator 1314. Because thefunctionality of the various components in FIG. 13 was described inrelation to FIG. 12 or would otherwise be well known by one of ordinaryskill in the art, additional description of the RF module layout is notprovided.

FIG. 14 illustrates an exemplary embodiment of a layout of thedevelopment module component of an UWB radio according to the presentinvention. Included in the development module component 1400 are thePower Input 1402, the Power Switch 1404, LEDs 1406 and 1408, an Ethernetconnection 1410, a RS-232 Input 1412, an RF Input 1414, Oscillators1416A-C, Correlators 1418A-B, Timers 1420A-B, a Baseband Processor 1422,a Processor 1424, a FPGA 1426, an Auxiliary Connector 1428, a RF ModuleInterface 1430. Also included in the Development module component 1400is an Ethernet MAC/PHY Interface, Flash storage and Memory. Because thefunctionality of the various components in FIG. 14 was described inrelation to FIG. 12 or would otherwise be well known by one of ordinaryskill in the art, additional description of the development modulelayout is not provided.

FIG. 15 illustrates an exemplary embodiment of a top-level systemsoftware architecture of the PLS according to the present invention. Asshown, a base station application 1504 is connected to a radiocontroller application 1516 to exchange data with the radio controllerapplication 1516 over a data network, such as Ethernet. Attached to theradio controller application 1516 is an antenna 1518 for communicatingwith a non-fixed node display application 1510. An antenna 1520 receivesa signal transmitted by the base station application 1504 and passes thesignal to a second radio controller application 1522. The second radiocontroller application 1522 passes information to the non-fixed nodedisplay application 1510.

In this embodiment, the PLS consists of three different applications;the base station application, the non-fixed display unit application,and the radio controller application. The Base Station applicationprovides a real-time display of node positions to users at the basestation. The non-fixed display application provides a user with a 2-D(or 3-D) display of each non-fixed node relative to one another. TheRadio Controller performs ranging between nodes and propagates distanceand position information through the network. These applications will bediscussed in FIGS. 16-19 below.

FIG. 16 illustrates an exemplary embodiment of a base stationapplication architecture according to the present invention. The BaseStation application architecture 1600 is software and/or hardwareincluded at the base station. The Base Station application 1504 may beexecuted on a laptop computer due to size and portabilityconsiderations, but may also be implemented using other computingdevices.

The Base Station Application 1600 architecture includes a Base StationApplication Manager 1608 residing on a computing device having aninterface to a network 1606 to which a UWB radio 1602 is connected. UWBradio transmits and receives UWB signals via antenna 1604. The network1606 may be an Ethernet network and may transport UDP packets. As such,the network connects the UWB radio and the computing device upon whichthe Base Station Application 1600 resides. Coupled to the Base StationApplication Manager 1608 are a Status Display Manager 1610, a Non-fixedNode Display Manager 1612, a Fixed Node Display Manager 1613, a 3-DDisplay Manager 1614, a 2-D Display Manager 1616, a Node InformationDisplay Manager 1617, and a Solver 1618.

In the present embodiment, the Base Station Application Manager 1608handles and stores all of the critical application data for tracking thelocation of primary, secondary, and non-fixed nodes. The Base StationApplication Manager 1608 also manages all critical event drivenprocesses of the PLS. The Base Station Application Manager 1608processes data communicated from the UWB radio 1604 over the Ethernet1606, such as data packets including alerts and ranges. In oneembodiment, the data packets are UDP database packets. The Base StationApplication Manager 1608 processes the alerts to modify an internal datastorage of the base station. Internal data storage stores the softwareused by the base station and stores range matrix information on thenodes.

The Base Station Application Manager 1608 also provides user interfacefunctionality. The Base Station Application Manager 1608 includessoftware for User Interface Processing to respond to inputs receivedfrom the user interface, such as displaying a dialog “pop-up” inresponse to a user requesting information on a particular node. A usermay view the particular node by selecting an icon representing theparticular node within a GUI via, for example, double-clicking on theicon.

The Base Station Application Manager 1608 also communicates with a 2-Ddisplay manager 1616. The 2-D Display Manager 1616 manages the displayand user interaction of a two-dimensional map view window of the GUI.The 2-D Display Manager 1616 displays a two-dimensional user-definedgrid, and user-defined icons that represent the nodes in their relativetwo-dimensional positions. The 2-D Display Manager 1616 also displaysother graphic interface objects, such as alert status icons, operationalstatus icons, or the like. The 2-D Display Manager 1616 processes userevents (e.g., zooming, panning, double-clicking, etc.) relative to theGUI.

The 3-D Display Manager 1614 communicates with the Base StationApplication Manager 1608, and manages the display and user interactionof the three-dimensional map view window of the GUI. The 3-D DisplayManager 1614 displays a three-dimensional user-defined grid, theuser-defined objects in their correct three-dimensional positions, aswell as other graphic interface objects using a software, such as, forexample, openGL. The 3-D Display Manager 1614 processes the user eventsrelative to the display window, such as zooming, panning,double-clicking, etc. In an alternative embodiment, the 3-D DisplayManager 1614 and the 2-D Display Manager 1616 may be incorporated into asingle display manager that can manage the display and user interactionof a two- and/or three-dimensional node map.

The Base Station Application Manager 1608 also communicates with a NodeInformation Display Manager 1617. The Node Information Display Manager1617 manages a pop-up dialog box containing detailed informationconcerning a selected node. The detailed information includes unit ID,name, node ID, position, operational status, alert status, order status,and icon descriptor.

The Non-fixed Node Display Manager 1612 communicates with the BaseStation Application Manager 1608, and manages the non-fixed node listview window of the GUI, which is a text listing of each non-fixed nodeand text data relative to the non-fixed node. The text listing of eachnon-fixed node and text data includes a name, node ID, alert status andoperational status.

The Fixed Node Display Manager 1613 communicates with the Base StationApplication Manager 1608, and manages the fixed node list view window ofthe GUI, which is a text listing of each fixed node and text datarelative to the fixed node. The text listing of each fixed node and textdata includes a node ID, operational status, an indication of whether aprimary or secondary reference node, time since last communication, andtime since last position update. It is noted that the time since lastposition text data for primary reference nodes does change because theirpositions do not change.

The Status Display Manager 1610 manages a status list view window withinthe GUI. The status list view is a list of text messages that displayevent information about the application as it happens. The statusdisplay manager maintains a scrollable history of the list of textmessages.

FIG. 17 illustrates an exemplary embodiment of the solver 1618 accordingto the present invention. The Solver 1618 is a application-independentmodule that is reusable across different tracking systems. The Solver1618 calculates the relative positions of the primary, secondary, andnon-fixed nodes based upon range matrix information received from theBase Station Application Manager 1608 during the ranging process. TheSolver 1618 uses triangularization to calculate the positions of theprimary, secondary, and non-fixed nodes within the PLS using the rangematrix information, as described above. The Solver 1618 also responds toposition update requests from the Base Station Application Manager 1608,and updates internal data storage with the position table updates.

As described below, the solver may filter ranging information to remove‘ranging noise’. Ranging noise can be described as the underlyingvariations in the ranging system that would cause variations inmeasurements over time as might be caused by temperature variations,interference, etc. Typically, if 100 measurements are taken, themeasurements will not all be the same and instead there will be anaverage measurement, standard deviation, etc. Such variations in thesame measurement over time are referred to here as ranging noise.Another type of ranging noise within the PLS occurs as a function ofrange measurements to a non-fixed node being taken at different times.This type of ranging noise comes into play whenever a non-fixed node ismoving. Accordingly, when needed as a secondary reference, a non-fixednode is requested to remain in a fixed location to remove this type ofranging noise.

The architecture of the Solver 1618 includes a Solver Class 1704, arange database 1712, an Active Reference/Device List 1714, and aPosition Database 1716. The Solver Class 1704 interacts with the RangeDatabase 1712, the Active Node List 1714, and the Position Database1712. Within the Solver Class 1704 is a Position Filter 1706, a PositionSolver 1708, and a Range Filter 1710.

The Range Filter 1710 processes range matrix information received fromthe Application Manager 1608 based on various factors, such as signalquality measurements on a communications link between a node pair, biterror rates, traveling speed of the nodes, and other additionalinformation (if available) on the node pair. The Range Filter 1710calculates acceptable range boundaries for the node pairs in accordancewith an established node speed limit and noise measurements. The RangeFilter 1710 then compares the range boundaries with the various factorsand with noise measurements on link quality. If the incoming rangematrix information is outside of the range boundaries, the Range Filter1710 replaces the incoming range matrix information with a previouslystored range matrix information, thereby filtering (or removing) rangematrix information outside of the acceptable range boundaries. Insteadof rejection range values, the range filter may modify range valuesusing different filtering techniques (e.g., extrapolation,interpolation, Kalman filtering) to correct erroneous range and alignranges taken at different points in time. When the range matrixinformation is outside of the range boundaries, the Position Solver 1708of the Solver 1618 retrieves a range history from the Range Database1712. The previous range matrix information may be based on the rangehistory for the node. The range history may be a single positioncalculation, an average position calculation, a statistical positioncalculation, or a position prediction based on range matrix informationreceived previously and stored in a Range database 1712 for the node.

The Position Solver 1708 uses the range history to calculate nodeposition based on the range history of the node and any current distanceinformation in the range matrix that is within the range boundary.Typically, the Position Solver 1708 first uses the current range matrixinformation in the position calculation. If the data is within the rangeboundary, the Position Solver 1708 performs the position calculation.However, the Position Solver 1708 may also use the range history tosupplement the current range matrix in the position calculation. Ifsufficient range information is available by combining the range historyand the current range matrix, a node position is calculated. If rangeinformation is insufficient even when using the range history, thePosition Solver 1708 may return duplicate solutions. Typically, therange information is insufficient when an insufficient number of nodesare tracking a node (i.e. less than two nodes), which causes duplicatesolutions of possible positions for a node. When this occurs, thePosition Solver 1708 assigns a probability to each of the possiblepositions and stores each of the positions with the respectiveprobabilities in the Position Database 1716. The probability is assignedto the possible locations based on information in the range history,and/or on a predicted location.

Once all of the node positions are calculated, then the Position Solver1708 develops a node map containing the relative positions of the nodes.The Position Solver 1708 then communicates the node map to the PositionDatabase 1716, which stores the current node map along with previousnode maps. After the Position Database 1716 receives the updated nodemap, the Position Database 1716 may signal the Position Filter 1706about the updated node map. The Position Filter 1706 may then request toreceive the updated node map from the Position Database 1716. Once thePosition Filter 1706 receives the updated node map, the Position Filter1706 sorts duplicate positions in the node map based on the positionhistory. In cases where no single solution exists for the position ofthe node, the Solver Class 1704 may query the user to enter a positionguess for the node to help with the decision. Once the duplicatepositions are sorted, the Position Filter 1706 places the node map in aposition table, which may be forwarded to the nodes.

Also interfacing with the Position Solver 1708 is the Active Node List1714. The Active Node List 1714 contains node identifications (IDs) thatdistinguish between individual nodes and node types (e.g. primary,secondary, non-fixed) in the PLS. The node types of the Active Node list1714 identify if a node is stationary, moving slowly, or moving quickly.The Active Node list maybe initially established by a user. In oneembodiment, the Active Node List remains constant while in anotherembodiment nodes may be added, deleted and/or their information modifiedin accordance with an established protocol.

When the Base Station Application starts, the Solver 1618 uses anauto-survey technique to determine the positions of the base stationrelative to the primary reference nodes, which have known locationsrelative to a reference point. The reference point may be a building orother structure that established a coordinate system. The coordinatesystem thus relates positions of the base station and the primaryreference nodes to the reference point. In one embodiment, a user isgiven rotational controls at the user interface to rotate the screen sothat it corresponds with the relative positions. In an alternativeembodiment, the system may auto-survey using known positions of fixedpoints that are entered into the base station, and the base stationdetermines its position relative to the fixed points. The fixed pointsmay be determined by, for example, a global positioning system.

Once the Solver 1700 has completed the auto-survey technique, the Solver1618 periodically receives range matrix information from the BaseStation Application 1600. In response, the Solver 1618 calculates a nodemap from the range matrix information, and communicates the node map tothe Base Station Application Manager 1608 in the form of a positiontable. The Base Station Application Manager 1608 then communicates nodemap to the 2-D Display Manager 1616 or the 3-D Display Manager 1614 fordisplay at the user interface. The base station application alsoforwards the position table (node map) to the UWB radio 1602, whichbroadcasts the position table to the other nodes in the network. Thenon-fixed nodes receive the position table and use it to update theirdisplays.

FIG. 18 illustrates an exemplary embodiment of a Non-fixed NodeApplication 1800 architecture of a non-fixed node according to thepresent invention. The Non-fixed Node Application 1800 architecture issimilar to the Base Station Application 1600 architecture. However, theNon-fixed Node Application generally does not include the solver 1618.Typically, the Non-fixed Node Application 1800 is used to display thepositions of the nodes received from the base station. In an alternativeembodiment, the Non-fixed Node Display Application includes a solver1618 for determining its position relative to other nodes.

The Non-fixed Node Application 1800 provides a user of a non-fixed nodewith a 2-D display of the relative positions of each primary, secondary,and non-fixed node's position. As shown, the Non-fixed Node Application1800 architecture includes an UWB radio 1802 equipped with an antenna1804. The UWB radio 1802 is attached to an Ethernet network 1806 forconnection to a Non-fixed Node Application Manager 1808. The Non-fixedNode Application Manager 1808 is coupled to a 2-D Display Manager 1816.The Non-fixed Node Application 1800 architecture may include a GUIsimilar to the GUI of the Base Station Application 1600, describedabove, including a 3-D display, status list view window, etc. ifdesired. In one embodiment, the Non-fixed Node Application 1800 executeson a Windows™ CE-based handheld computer.

The Non-fixed Node Application Manager 1808 of the Non-fixed NodeApplication 1800 architecture handles and stores all criticalapplication data and all critical event driven processes. The Non-fixedNode Application Manager 1808 processes the critical application datareceived from the Ethernet 1806, which may be data packets, such as, forexample, UDP database packets, received on positions or on alerts formthe base station. The Non-fixed Node Application Manager 1808 processesthe alerts to modify internal data storage and notify the non-fixed nodeif an assist alert or an evacuation has been ordered received from thebase station. Critical event driven processes include an assist messageand an evacuation message. The Non-fixed Node Application Manager 1808also performs user interface functions based upon user interface drivenevents such as a MAYDAY alert event which may result in a non-fixeddevice vibrating, flashing a light, emitting a sound, or any combinationof these.

Coupled to the Non-fixed Node Application Manager 1808 is the 2-DDisplay Manager 1816. The 2-D Display Manager 1816 handles the displayand user interaction in a map view window. The map view window is adisplay of the user-defined grid and the user defined icons. In the mapview window, the user-defined icons are placed at locations thatcorrespond to the relative positions of the base station and each of thenodes. The user-defined icons may also display node ID information, atwo dimensional coordinate position of the node (x, y), speed of thenode, or any other information on the user of the node or its movementcharacteristics. The 2-D Display Manager 1816 also processes user eventsrelative to the display window, including zooming, panning, etc. In analternative embodiment, a 3-D Display Manager may be used to display athree dimensional representation of the nodes.

At startup, the 2-D Display Application is adapted to receive a positiontable from a primary reference node at the attached UWB radio 1802. The2-D Display Application periodically receives updates of the positiontable from the UWB radio via the Non-fixed Node Application Manager1808. The 2-D Display Application also receives and displays alerts fromthe base station, and broadcasts alerts from the user (e.g., afirefighter).

FIG. 19 illustrates an exemplary embodiment of a radio controllerapplication according to the present invention. The radio controllerapplication performs ranging between nodes and propagates range andposition information throughout the PLS. The radio controllerapplication is an embedded application that executes on each node in thePLS network. Primary reference nodes, secondary reference nodes andnon-fixed nodes all may run the same radio controller application.

The radio controller architecture includes a range manager 1908, a rangedatabase 1910, a socket manager 1912, a Time Division Media AccessController (TDMAC) 1902, and an antenna 1904. The range manager 1908 isa control system that decides which nodes to range with and responds torange requests from other nodes. The range manager 1908 selects a nodeto range with based on a number of criteria, including signal strength,link quality, bit error rate, or other known signal quality parameters.The range manager 1908 also merges range matrices received from othernodes into the range database 1910, and routes data between the socketmanager 1912 and the TDMAC 1902.

The range database 1910 is a table of the most current ranges known to anode in the range matrix. Each range has an age defined by a time stampand older ranges are replaced by updated range matrix information whenit is received.

Coupled to the Socket Manager 1912 is a connection to an Ethernet 1906.The socket manager 1912 manages Ethernet traffic over a UDP socket. Thesocket manager 1912 receives the position table from the Base Station,and transmits a range matrix to the base station.

The present embodiment may support a variety of air-time schedulingmethods, including Time Division Multiple Access (TDMA) and CarrierSense Multiple Access (CSMA). Generally, any air-time scheduling methodthat allocates a given time slot, frequency slot, or code to a givennode may be used. In this embodiment, the radio controller architecture1900 includes a Time Domain Medium Access Controller (TDMAC) 1902attached to an antenna 1904. The TDMAC 1902 interfaces with the Rangemanager 1908, and coordinates the access of all nodes to a wirelessmedium using air-time scheduling methods. The TDMAC supports severalmeans of providing access to the wireless medium. In one embodiment, thePLS uses a TDMA scheme. The TDMA scheme divides air time into frames(also called time slots) and aggregates frames into superframes. Eachradio is allocated a pre-defined time slot for transmitting data. Eachtime slot is large enough to accommodate both packets in a rangingsequence (a request packet followed by a response packet). Thesuperframe is large enough to contain one time slot for each radio inthe network.

In an alternative embodiment, a CSMA controller may be used. The CSMAcontroller detects whether any other nodes are transmitting, and if theyare, the CSMA controller waits a random amount of time, and then detectswhether any other nodes are transmitting. If no other nodes aretransmitting, the CSMA controller allows the node to transmit.Otherwise, the CSMA controller waits another random amount of time.

FIG. 20A illustrates an exemplary embodiment of a time division multipleaccess (TDMA) superframe and time slot according to the presentinvention. Each superframe 2002A-N contains ‘n’ times slotscorresponding to the ‘n’ nodes, where time slot 0 is occupied by Node 0.The time slots may correspond to the node IDs. As shown, the Time Slotfor Node n−1 includes a number of smaller time slots 2020. The time slot2020 includes a Sync Packet 2022, a Request Packet 2024 and a ResponsePacket 2026. Time slot 2020 is an exemplary embodiment of range matrixinformation in the PLS network.

At startup, the TDMAC 1902 of each node is configured with its ownunique time slot in the superframe 2002. In an alternative embodiment,the base station may assign each node a time slot. At the beginning ofthe time slot for each node, the range manager 1908 of each node selectsanother node to range with based on the length of time between the lastranging measurement with that node. The range manager 1908 of the nodetransmits a range request packet 2024 when desiring to range with aparticular node, and receives a range response packet 2026 from thatparticular node. Based on the transmitted and received packets, theradio calculates the distance to the other node based on information inthe response packet.

In the PLS, each node listens to all of the time slots in eachsuperframe 2002. In one embodiment, each node listens in the rangerequest packet 2024 time slot for their node ID. If the range request2024 includes their node ID, the receiving node transmits a rangeresponse packet 2026 that includes a node ID of the transmitting nodethat sent the range request packet 2024. After receiving their node IDin the range request packet 2024, the receiving node extracts the rangematrix 2056 and the position table 2058 from the range request packet2024. The receiving node uses the range matrix 2056 and the positiontable 2058 to update its range database 1910, and then transmits theupdated range matrix 2056 and position table 2058 out a UDP socket to bebroadcast to other nodes.

FIG. 20B illustrates an exemplary embodiment of the range request packet2024 according to the present invention. Included in each range requestpacket 2024 is a location for acquisition part 2050, a header 2052, akernel header 2054, a range matrix 2056, a position table 2058, andmultiple scan ramps 2060 in the ranging process. The acquisition part2050 is a known data pattern that can be searched for and synchronizedwith to acquire the request packet. The header 2052 and the kernelheader 2054 are used to define the structure of the remainder of thedata within the packet. The range matrix 2056 contains all ranges toother nodes known to the transmitting node and their respective nodeIDs. The Position Table 2058 includes the latest version of the node maptransmitted from the base station. The multiple scan ramps 2060 allowfor signal quality comparison over time.

As an alternative to the centralized position solver approach describedpreviously, a distributed solver approach can be employed whereindividual nodes determine their own position. Under this arrangement,individual nodes initiate ranging with reference nodes about them and,after ranging with those nodes, use ranges measured to those nodes todetermine their own position, which is then communicated to the othernodes via the position table. Under this arrangement, range matrixinformation does not have to be shared among nodes. Furthermore, a nodecan transmit a single ‘multiple ranging request packet’ that includes alist of those nodes to which it requests a range measurement. Uponreceiving the multiple ranging request packet, each node included in thelist can provide an acknowledgement message to the requesting node aftera predefined delay corresponding to its position in the list. Therequesting node can accordingly subtract the corresponding delays fromthe ranging measurements to the requested nodes to determine the timesof flight and corresponding ranges to the nodes.

FIG. 21 illustrates an exemplary embodiment of a computing environment2100 for the PLS according to the present invention. The computingenvironment may be implemented at each of the base station and at thenodes. However, certain display components described below may only beincorporated into the base station or the non-fixed nodes, but may alsobe included in primary and secondary reference nodes. As shown, aCommunication Infrastructure 2106 interfaces with a Display Interface2102, a Main Memory 2108, a Secondary Memory 2110, a CommunicationsInterface 2124, and a processor 2104. The Communication Infrastructureis adapted to communicate data between the various devices.

The display interface 2102 is further coupled to a Display 2130. Thedisplay interface is adapted to receive and process the node map, and toplace the node map in the map view window of the GUI. The displayinterface 2102 outputs a display signal to the display 2130 to displaythe node map to the user.

The secondary memory 2110 is further comprises a hard disk drive 2112, aremovable storage drive 2114, and an interface 2120. The secondarymemory 2110 is further coupled to the removable storage units 2118 and2122. The secondary memory 2110 is the storage device for the node orbase station, and stores, for example, the range matrix informationexchanged in the PLS, as well as other necessary software forimplementing the other functions of the base station and nodes.

The Communications Interface 2124 is further coupled to theCommunications Path 2126 through cable 2128.

FIG. 22 illustrates an exemplary process performed by the PLS accordingto the present invention. In step 2202, a primary reference node isplaced at a first position. In step 2204, a secondary reference node isplaced at a second position, and the secondary reference node and theprimary reference node communicate using, for example, UWB signals. Instep 2206, a first range between the primary reference node and thesecondary reference node is determined. In step 2208, the secondaryreference node receives a first communication from a non-fixed node.

In step 2210, a second range between the secondary reference node andthe non-fixed node is determined. In step 2212, the primary referencenode receives a second communication from the non-fixed node. In step2214, a third range between the primary reference node and the non-fixednode is determined. In step 2216, one or more locations for thenon-fixed node is determined from at least the first communication orthe second communication. In step 2218, a node map is formed thatincludes positioning information about the non-fixed node, the primaryreference node, and the secondary reference node.

In step 2220, the one or more locations are resolved to an actuallocation by using one or more quality measures associated with the rangematrix information. In step 2222, additional communications are receivedfrom the non-fixed node. In step 2224, changes in the range matrixinformation of the non-fixed node are tracked. In step 2226, the map isupdated based on the changes in the range matrix information.

FIG. 23 illustrates an exemplary process of performing distancecalculations by using a non-fixed node as a secondary reference node fora certain period of time according to the present invention. In thisembodiment, the exemplary process follows steps 2202-2210 in FIG. 22,and then after step 2210 proceeds to step 2302. In step 2302, thenon-fixed node is converted into an additional secondary reference nodefor a period of time. In step 2304, the additional secondary referencenode receives a second communication from an additional non-fixed node.In step 2306, a third range is determined between said additionalsecondary reference node and the additional non-fixed node.

FIG. 24 illustrates another exemplary process of using a non-fixed nodeas a secondary reference node for a certain period of time according tothe present invention. The exemplary process follows steps 2202-2216 inFIG. 22, and then after step 2216 proceeds to step 2402. In step 2402,the non-fixed node is converted into an additional secondary referencenode for a period of time. In step 2404, the additional secondaryreference node receives a third communication from an additionalnon-fixed node. In step 2406, a fourth range is determined between saidadditional secondary reference node and the additional non-fixed node.In step 2408, range matrix information is obtained about the additionalnon-fixed node from one or more of the primary or secondary referencenodes.

In step 2410, a node map is produced that includes range matrixinformation about each primary, secondary, and non-fixed node and alsoincludes a relative position of each. In step 2412, range matrixinformation is received from one of the primary, secondary, or non-fixednodes. In step 2414, the range matrix information is evaluated for a setof positions of least error regions. In step 2416, the node map isupdated with the set of positions. In step 2418, one or more combinedsets of positions is determined, and the primary, secondary, andnon-fixed nodes are not necessarily uniformly providing range matrixinformation.

It is noted that the present invention may be used in firefighter andwarfare situations. The present invention is also particularly useful inthese situations since the PLS is a man deployable UWB system thatprovides easily interpreted, real-time, highly accurate positionlocation information to both a user carrying a non-fixed device, as wellas incident command personnel who may be located at the base station, orat another remote location. The base station of the PLS may be used byas a command center where incident command personal track and direct themovement of troops or firefighters within a building. The base stationmay forward commands, such as go to position X, to identify the locationof a non-fixed node user in need, or to order an evacuation of abuilding.

Also, the number of primary reference nodes, secondary reference nodes,base stations, and non-fixed nodes described above is for illustrativepurposes. A greater or lesser number of nodes may be used withoutdeparting from the spirit and scope of the invention. As describedpreviously, primary reference nodes may be placed about a coverage areaas required to achieve an expected acceptable level of confidence inranging measurements. Accordingly, non-fixed nodes and secondaryreference nodes located at calibration points and acceptance levelscoring criteria can be used to optimize primary reference nodelocations so as to provide a sufficient number of primary nodes toachieve acceptable ranging accuracy.

It is further noted that the present invention may be used in monostaticand/or bistatic radar array applications where single nodes or pairs ofprimary reference nodes, secondary reference nodes, and/or non-fixednodes perform monostatic radar and/or bistatic radar functions asdescribed in U.S. Pat. No. 5,363,108 (issued Nov. 8, 1994) to Fullerton,U.S. Pat. No. 6,177,903 (issued Jan. 23, 2001) to Fullerton et al., U.S.Pat. No. 6,218,979 (issued Apr. 18, 2001) to Richards, and U.S. Pat. No.6,614,384 (issued Sep. 2, 2003) to Hall et al., all of which areincorporated herein by reference in their entirety.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. Thus, the breadth and scope of thepresent invention should not be limited by any of the above-describedexemplary embodiments, but should instead be defined only in accordancewith the following claims and their equivalents.

1. A method for determining a position of an ultra wideband (UWB) radio,comprising: determining using a processor a plurality of positionscorresponding to a plurality of reference UWB radios; determining usinga processor a plurality of confidence metrics corresponding to saidplurality of positions; selecting using a processor a plurality ofacceptable positions based upon said plurality of confidence metrics andan acceptance criteria; and determining using a processor said positionof said UWB radio based upon said plurality of acceptable positions,said processor outputting to an interface said position of said UWBradio.
 2. The method of claim 1, wherein said acceptance criteriaprovides a highest possible confidence level of said position of saidUWB radio.
 3. The method of claim 1, wherein at least one of saidplurality of positions is determined based upon a UWB signaltransmission.
 4. The method of claim 3, wherein said UWB signaltransmission is one of a one-way signal transmission or a round-tripsignal transmission.
 5. The method of claim 1, wherein at least one ofsaid plurality of reference UWB radios is non-fixed.
 6. The method ofclaim 1, wherein said UWB radio is capable of transmitting UWB signalsand said UWB radio is not capable of receiving UWB signals.
 7. Themethod of claim 1, wherein each of said plurality of confidence metricscomprises at least one of a range measurement quality metric, a standarddeviation, a measurement age metric, an error region metric, a signalquality metric, an RF environment metric, or a ranging geometry metric.8. The method of claim 7, wherein said ranging geometry metric comprisesat least one of an angle acuteness metric or a geometric dilution ofprecision metric.
 9. The method of claim 1, wherein the non-existence ofa direct path between said UWB radio and at least one of said pluralityof reference UWB radios is identified.
 10. The method of claim 1,wherein a confidence level of said position indicates a requirement forone or more additional reference UWB radios to achieve an acceptablesaid confidence level.
 11. The method of claim 1, wherein said UWB radiois a secondary reference UWB radio.
 12. The method of claim 1, furthercomprising: filtering ranging noise prior to determining at least oneposition.
 13. The method of claim 1, further comprising: positioningsaid plurality of reference UWB radios at locations intended to provideacceptable position determination accuracy over a coverage area.
 14. Themethod of claim 1, further comprising: positioning said plurality ofreference UWB radios such that said UWB radio is always within at leasta desired distance from a closest reference UWB radio of said pluralityof reference UWB radios.
 15. The method of claim 1, wherein saidacceptance criteria comprises at least one of a acceptability thresholdor a decision tree.
 16. The method of claim 1, wherein said acceptancecriteria comprises at least one of a threshold, a decision tree, a workload, a number of times an error region has compounded, a line-of-sightcharacteristic, a speed, a direction, an elevation, a speed in change ofspeed, a speed in change of direction, or a speed in change ofelevation.
 17. The method of claim 1, wherein at least one of saidplurality of reference UWB radios comprises a primary reference UWBradio.
 18. The method of claim 1, wherein at least one of said pluralityof reference UWB radios is positioned by one of a robot, a soldier, afirefighter, a police officer, or an emergency responder.
 19. A systemfor determining a position of an ultra wideband (UWB) radio, comprising:a plurality of reference UWB radios corresponding to a plurality ofpositions; and at least one processor that determines a plurality ofconfidence metrics corresponding to said plurality of positions, selectsa plurality of acceptable positions from said plurality of positionsbased upon said plurality of confidence metrics and an acceptancecriteria, determines said position of said UWB radio based upon saidplurality of acceptable positions, and outputs said position of said UWBradio to an interface.
 20. A method for determining a position of anultra wideband (UWB) radio, comprising: determining using a processor aplurality of position confidence metrics corresponding to a plurality ofreference UWB radio positions; selecting using a processor a pluralityof acceptable reference UWB radio positions from said plurality of UWBradio positions based upon said plurality of position confidence metricsand an acceptance criteria; and determining using a processor saidposition of said UWB radio based upon said plurality of acceptablereference radio positions, said processor outputting to an interfacesaid position of said UWB radio.